The present invention relates to a new and improved method of regulating the bath level of a continuous casting mold by means of electromagnetic alternating fields, wherein there are measured changes of the inductance as a function of the bath level which are used as input signals for regulation of the bath level. The invention further pertains to new and improved constructions of apparatus for the performance of the aforementioned method aspects.
For the automatic regulation of the bath level of continuous casting molds, especially continuous casting installations for steel, there have become known to the art different methods which have been employed in practical applications. Measuring the bath level by means of radioactive devices, thermoelements, optical devices and so forth have found widespread use in this technology.
Publications concerned with the continuous casting art have also proposed measuring the change in the bath level of the continuous casting mold by means of electromagnetic alternating fields. According to specific proposals in this respect one or a number of coils are arranged externally of the cooling jacket at the region of the bath level or over the entire length of the mold about the mold walls and generate an electromagnetic alternating field. The liquid casting metal functions as a movable coil core and as the bath level changes produces changes in the electromagnetic alternating field. At one or a number of receiver coils these changes of the inductance are measured as a function of the bath level and employed as an input signal for regulation of the bath level. These proposed apparatuses are associated with the drawback that the input signal is appreciably affected to a greater degree owing to continuously changing disturbing influences than by the changes in the level of the molten bath in the continuous casting mold. With changes in the bath level of, for instance, 1 centimeter, with a measuring system having coils arranged about the mold, there were measured as characteristic values less than 0.1 percent change in relation to the output inductance. Such small differences in the measured value as the input signal for a control produce inaccurate output signals for the regulation of the inflowing molten metal. Moreover, temperature differences at the copper wall and in the supporting frame cause changes in the mutual inductance between the coils in the order of magnitude of about one percent. These disturbing influences due to superimposing phenomena attenuate and falsify the measuring results to such a degree that they are no longer suitable for accomplishing an exact regulation of the molten bath level. It is for these reasons that such measuring technique has not found any practical application in the continuous casting art up to the present time.